Milk Quality Lecture Materials

INTRODUCTION TO DAIRY SCIENCEPAUL EBNER , ASSOCIATE PROFESSOR, PURDUE ANIMAL SC IENCES

PRODUCED FOR THE USWDP FOOD TECHNOLOGY BR IDGE PROGRAM AT HEART UNIVERSITY

Afghanistan Milk Statistics# of total cattle (cows):

3.7 million

# of milking cows:2.2 million

Kilos of milk produced each year:945,000 t

Average yearly milk consumption:66 kilos/person

U SWD P F O O D T E C H N O L O G Y B R I D G E P R O G R A M AT H E R AT U N I V E R S I T YPAUL EBNER, PHD, PURDUE UNIVERSITY

Dairy Science• Dairy: every product made primarily from milk from all species of mammal-‐including milk• Milk• Powdered or dry milk• Separated cream• Dried whey• Butter• Ice Cream• Yogurt• Solid yogurts• Semi-‐solid yogurts• Drinkable yogurts• And much more!


Milk Production Basics• Milk is highly nutritious• Close to a “perfect food”

• Milk is easily converted to value-‐added products• Examples: yogurt, cheese, butter, cream, etc.• Can increase profit• Can increase shelf-‐life


CHARACTERISTICS OF MILK

USWDP F O O D T E C H N O L O G Y B R I D G E P R O G R A M AT H E R AT U N I V E R S I T YPAUL EBNER, PHD, PURDUE UNIVERSITY

Solids in Milk• Milk is approximately 87% water• Milk solids: everything that makes up the remaining 13%• Total solids: all solids together• Solids, non-‐fat: all solids excluding the fat portion


Solids in Milk• The solids of milk are what distinguishes milk from water. • Protein: heavier than water• Sugars: heavier than water• Fat: lighter than water• Result: Milk is always heavier than water

• Density of milk is determined by measuring its specific gravity


Solids in Milk• Measuring the density of milk is easy• Done with a lactometer• Lactometer: hydrometer for milk• Can quickly and easily tell if something is added to milk based on density• We will do this in the lab


Solids in Milk• Typical composition of raw milk:• Water: 87%• Fat: 4%• Protein: 3.5%• Sugars: 4.0%• Vitamins/minerals: < 0.5%

• Total solids = ??• Solids, non-‐fat = ??


Solids in Milk• The composition of milk can significantly affect production of dairy products• Some yogurts require < 3.0% fat• Some yogurts require higher protein

• The composition of raw milk is heavily dependent on:• Animal genetics: for example, some species and breeds within species produce higher fat milk

• Animal feeding: high quality diets = high quality milk


Solids in Milk• Fortunately, the composition of raw milk can be changed with some basic math• Example: • Have 3.8% fat milk• Have skim milk (~0.1% fat)• Need 3.0% fat milk


Solids in Milk• Skim milk: ~0.1% fat

Pearson’s Square

3.0

3.8

0.1

2.9

0.8

So, to make 3.0% milk from 3.8% milk and 0.1% milk, you would add:0.8 L of 0.1% milk to2.9 L of 3.8% milk


pH• pH of good quality, raw milk is ~6.4 – 6.7• Knowing the proper pH of milk is very important for both quality and processing• Low pH:• Indication of spoilage and growth of bacteria (reduces shelf-‐life and profit)

• Interferes with yogurt, cheese production


Basic Science of Yogurt• Chemically, when milk becomes yogurt it is changing from an emulsion to a colloid

• Emulsion: a mixture of two liquids, like oil and water. “Emulsion” comes from the latin word for “milk”. Milk is an emulsion of water and oil (milk fat)

• Colloid: a dispersion of solid particles in a liquid


Basic Science of Yogurt

RAW MILK Emulsion of water

and fatpH: 6.5

% acidity: 0.17

Heated to 85C and cooled to ~45C

COOKED MILKStill an emulsion

No change in acidity

Bacterial culture added and incubated at 45C

YOGURTColloid of water and solid (protein)

pH: 4.0% acidity: 1.0

What exactly happened??


Basic Science of Yogurt• The predominant protein in milk is casein• In raw milk casein forms micelles• Bacterial growth results in acid production• Acid (low pH) breaks up micelles• Casein then forms a net that traps water


Basic Science of Yogurt• So, yogurt has

approximately the same composition of water, fat, protein, and sugar as raw milk, but the proteins (casein) have formed a net that traps water

• The water that you sometimes see on top of yogurt is just water that has escaped the trap!


Microbial Component of Milk• Raw milk is never sterile• Bacteria (and other microorganisms) enter milk during collection:• From the environment• From animal itself• From the milker

• Pasteurization is designed to controlmicrobial populations


Microbial Component of Milk• Pasteurization is designed to controlmicrobial populations• Pasteurization parameters:• Batch: 63C for 30 min• Continuous: 72C for 15 sec

• Destroys pathogens• Many types of bacteria can survive pasteurization


Microbial Component of Milk• UHT: Ultra-‐High Temperature Pasteurization• > 135C for 1-‐2 seconds• Designed to kill ALL bacteria including spores• UHT milk has a shelf-‐life of about 6 – 9 months (if unopened)


Microbial Component of Milk

Pasteurization System


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Microbial Component of Milk• APC is used throughout the world to measure microorganisms in milk• Also called, TPC, VPC, etc. Essentially the same thing• TPC: Total Plate Count• VPC: Viable Plate

• Some standardsRaw Milk Pasteurized Milk

APC <106 CFU/mL <200 CFU/mLColiforms <200 CFU/mL undetectable


Microbial Component of Milk• Because pasteurization does not kill all bacteria, very high initial bacteria counts in raw milk usually translate to unacceptably high bacteria counts even after pasteurization

• If initial counts are high (e.g., 107). Pasteurization may only reduce concentration to 103 – 104, then the remaining bacteria will grow to high concentrations very quickly

• High bacterial counts = quick spoilage = reduced shelf-‐life = loss of profit

• 7-‐10 days: shelf-‐life of high quality, pasteurized milk under refrigeration


Mastitis• Mastitis: inflammation/infection of the udder


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Mastitis• Mastitis in milk producing animals is a world-‐wide problem:• More contamination of milk (many mastitis causing organisms are also human pathogens)

• Reduced quality of milk• Reduced profit• Animal welfare

• Most of the time mastitis is controlled by proper sanitation and hygiene of the milking environment

• In severe cases, animals have to be treated with antibiotics


Mastitis Tests• Somatic Cell Count (SCC): test of quality of milk

• Somatic cells are mostly leukocytes

• The number of leukocytes increases when there is an infection

• These cells are “shed” from the udder to milk

• High Somatic Cell Counts in milk indicate the cow may have mastitis

• SCC < 300,000 indicates mastitis

• Good, quality milk should be < 100,000


Milk Composition and Quality Tests• Worldwide, the most common and standard milk tests are:• 1. APC• 2. SCC• 2. Coliforms• 3. pH/acidity %• 4. Fat content• 5. Protein content

• Knowing how and WHY you do these tests is critical in measuring and understanding milk quality


ADULTERATION OF MILK

USWDP F O O D T E C H N O L O G Y B R I D G E P R O G R A M AT H E R AT U N I V E R S I T YPAUL EBNER, PHD, PURDUE UNIVERSITY

Adulteration• Adulteration: adding anything to milk, intentionally or unintentionally, that changes the composition, quality, or safety of milk

• Compounds used in adulteration are referred to as adulterants

• Milk is one of the most nutritious foods available, unfortunately it is also one of the easiest to adulterate


Adulteration• Unintentional adulteration: antibiotic residues, detergents left in milk containers for washing

• Intentional adulteration is deliberate and done to make the milk appear that it is higher quality, more fresh, higher volume than it really is. It is done to cheat milk buyers and consumers• Result can be reduced milk quality and nutrition. In severe cases, people have died from adulterated milk


Examples of Adulteraton• Antibiotic residues• Usually a case of unintended adulteration• Antibiotics are used to treat a sick animal and are easily passed to the udder and to milk• This is common if the milk producer does not understand antibiotic use• Milk from cows receiving antibiotics should be discarded or used for animal feed, etc.


Examples of Adulteraton• Problems caused by antibiotic residues:• 1) Safety: at high concentrations it can be a health hazard• 2) ??


Examples of Adulteraton• Water• Adding water is done simply to increase volume• Milk is sold to stores and to consumers based on weight or volume• Milk that is >25% added water can have the same appearance as regular milk (higher in the case of skim milk)


Examples of Adulteraton• Water• Positive: adding water reduces the density of milk and is easily detected with a lactometer• Negative: adding a second compound to milk adulterated with water can increase the density giving the appearance of normal milk• We will see this in the lab


Examples of Adulteraton• Preservatives• Preservatives are regularly used in food production• They should never be added to milk• Adding preservatives:• Reduces bacterial growth giving the milk the appearance that it is fresh when it could be very old

• Reduces the ability to make any fermented dairy product (e.g., yogurt, cheese, etc.)

• Some commonly used preservatives are somewhat harmless (citric acid) while others are very dangerous (formaldehyde)


Examples of Adulteraton• pH buffers• Buffer: a compound that prevents large changes in pH• Example: sodium carbonate, used in food production, but should never be in milk• When added, bacteria may grow, but there will be no change in pH (even though acid is being produced)• Result:• Old milk looks like new milk• Milk cannot be used for fermented products


Examples of Adulteraton• Unfortunately, there is a long list of adulterants that can be used in milk to make it appear more nutritious, fresher, etc.

• Other examples include:• Adulterants that make milk appear to have more cream (soap)• Adulterants that make milk appear to be higher in fat (vegetable oil)

• Adulterants that make milk to be higher in protein (melamine)

• Adulterants can significantly reduce the quality, safety, and usability of milk = loss of profit


Documents

Milk Quality Lecture Materials